CN111925271A

CN111925271A - Catalytic decomposition method for preparing propylene by direct dehydrogenation of propane

Info

Publication number: CN111925271A
Application number: CN202010827278.1A
Authority: CN
Inventors: 徐文涛; 王祈歌; 周继承; ***
Original assignee: Xiangtan University
Current assignee: Xiangtan University
Priority date: 2020-08-17
Filing date: 2020-08-17
Publication date: 2020-11-13
Anticipated expiration: 2040-08-17
Also published as: CN111925271B

Abstract

The invention provides a catalytic decomposition method for preparing propylene by direct dehydrogenation of propane, which comprises the steps of forming a catalytic reaction bed by using a composite non-noble metal catalyst in a microwave reactor, and carrying out gas-solid phase microwave catalytic reaction on propane-containing gas through the catalytic reaction bed so as to realize the direct dehydrogenation of propane to prepare propylene; the composite non-noble metal catalyst does not contain noble metals such as gold, silver, ruthenium, rhodium, palladium, osmium, iridium and platinum, and is a Co-Sn/NC catalyst, namely the active component of the catalyst is metal cobalt, the promoting component is tin, and the carrier of the catalyst is a nitrogen-containing carbon carrier. The invention solves the problem of lower activity of non-noble metal catalysts in the prior art. The method has the advantages of mild reaction conditions, high propane conversion rate and propylene selectivity, simple reaction operation, low energy consumption and low cost. The invention utilizes abundant alkane resources to prepare propylene and hydrogen, and maximally utilizes the alkane resources.

Description

Catalytic decomposition method for preparing propylene by direct dehydrogenation of propane

Technical Field

The invention relates to the technical field of propane dehydrogenation to propylene catalysis, in particular to a method for preparing propylene and hydrogen by directly dehydrogenating propane through microwave catalysis.

Background

Propylene is a petrochemical product which is the second important product except ethylene, is used as a basic raw material of three large synthetic materials (plastics, synthetic fibers and synthetic rubber) and is also a main raw material of bulk chemical products such as acrylonitrile, propylene oxide, acrylic acid and the like, and downstream requirements cover the fields of military industry, pharmacy, textile, medical treatment and the like. In 2017, the total yield of propylene in China is reported to be 2.8 million tons, the net import yield of propylene reaches 309 million tons, the total quantity of downstream demand is over 3.2 million tons, and the propylene market is in a short supply and short demand state for a long time. The traditional propylene production processes are mainly steam cracking and fluidized bed catalytic cracking. In both processes, propylene is obtained through a byproduct, and the yield is too low to supply huge demand due to the restriction of the production of ethylene and oil products. In addition, by means of abundant coal resources, the method for preparing the propylene from the coal has considerable profit after industrialization, and the technology for preparing the propylene from the coal is widely applied to industrialization. However, in recent years, due to policy adjustment, coal prices have greatly increased, and the price center of gravity of propylene has moved downward, so that the profit of the coal-to-propylene process is far less than before. The low-carbon alkane is mainly derived from shale gas, oilfield associated gas and the like, has rich reserves and low price, and is used as low-value fuel all the time. The propane dehydrogenation process has excellent economic benefits due to the price difference between propane and propylene. In recent years, shale gas and natural gas are also different from military projects, so that a process method for preparing olefin by using low-alkane as a raw material becomes a good-standing new propylene production technology with the fastest market share and the most prospect. The existing mature process for preparing propylene by propane dehydrogenation comprises an Olefiex process of UOP company in the United states and a Catofin process of Lummus company. The Olefield process adopts platinum catalyst, the reaction condition is 550-650 ℃, propane is dehydrogenated under the hydrogen condition, the conversion per pass can reach 30-40%, and the selectivity is 89-90%. However, Pt is expensive, has high requirement on the purity of reaction raw materials, is easy to deposit carbon and coke in the reaction process, covers partial active sites and deactivates the catalyst; the reaction temperature of the Catofin process is 560-650 ℃, the catalyst is a chromium catalyst, the conversion per pass can reach 48-65%, and the propylene selectivity is 88%. However, Cr, as a heavy metal, not only causes serious pollution to the environment, but also harms human health. The existing 12 sets of propylene production lines adopting propane dehydrogenation are introduced from foreign countries at high price, catalysts are completely imported, and the propylene industry in China forms a passive situation of 'neck' of developed countries in Western countries. Therefore, development of a new green inexpensive type propane dehydrogenation catalyst and a propane dehydrogenation process have appeared to be of great importance.

The technology for preparing olefin by propane dehydrogenation mainly comprises oxidative dehydrogenation and direct dehydrogenation. The former belongs to exothermic reaction at low temperature in thermodynamics, does not need harsh reaction conditions, but the existence of oxygen-containing species enables the target product propylene to be easily deeply oxidized, the target product has low selectivity and is not easy to desorb, and the reaction activity and the selectivity are very poor, which is also the reason that the industrialization of propane oxidative dehydrogenation cannot be realized at present. Compared with oxidative dehydrogenation, the direct propane dehydrogenation process has higher selectivity, low equipment cost in industrial production and wide application in generating clean energy hydrogen, but the process is influenced by thermodynamic balance and has strong endothermic reaction. According to the le chatelier principle, the improvement of the alkane conversion rate is excessively dependent on high temperature and low pressure, but the C-C bond is more reactive than the C-H bond under the high temperature condition, which in turn can cause the occurrence of unnecessary side reaction, even the carbon deposition and the coking sintering of the catalyst. In addition to platinum-and chromium-based catalysts, researchers are constantly trying to develop other families of catalysts. Hu et al (ChemCatchem, 2017.) reported a mesoporous CoAl₂O₄Spinel catalysts, when used in propane dehydrogenation reactions, have approximately 5% conversion and 80% selectivity at 550 ℃. In addition, Hu et al (Journal of Catalysis, 2015, 322:24-37.) also prepared a single-site Co²⁺/SiO₂The catalyst shows good stability and activity in 24h continuous propane dehydrogenation (about 95% selectivity at 550 ℃ and 90% reduction at 600 ℃). Sun et al (Catalysis Letters, 2015, 145(7):1413-²⁺The active site of dehydrogenation reaction is formed in the course of ion reaction, and its high load (A)>10 wt.%), Co₃O₄The crystals are easily reduced to metallic Co species resulting in cracking reactions that produce large amounts of methane. However, Li et al (Applied Surface Science, 2018.) found that when Co-based catalysts were used in the propane dehydrogenation reaction, both the pre-reduced catalyst and the fresh catalyst had an induction transition period, while the pre-oxidized catalyst initially exhibited high selectivity (-90%), was not easily deactivated, and was also stable. The university of southeast university topic group (Journal of Materials Science, 2014, 49(3):1170-₂O₄So that part of Mg⁺、Al⁺Enters the ZSM-15 molecular sieve to change the acid property of the carrier and find that when MgAl is used₂O₄When the/ZSM-15 mass ratio is 3, the catalyst has higher catalytic activity and stability, and the carbon deposition amount on the catalyst is greatly reduced. From the Co catalysts reported in research literature, we can see that the non-noble metal Co catalysts have high selectivity and unsatisfactory conversion rate when used in the propane dehydrogenation reaction, and the reaction temperature is high (550-600 ℃). Therefore, a new propane dehydrogenation process has yet to be developed to address these difficulties.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provide a method for preparing propylene and hydrogen by catalyzing propane dehydrogenation, which has mild reaction conditions, simple process and low cost.

Therefore, the invention provides a catalytic decomposition method for preparing propylene by direct dehydrogenation of propane, which comprises the steps of forming a catalytic reaction bed by using a composite non-noble metal catalyst in a microwave reactor, and carrying out gas-solid phase microwave catalytic reaction on propane-containing gas through the catalytic reaction bed so as to realize the direct dehydrogenation of propane to prepare propylene; the composite non-noble metal catalyst does not contain noble metals such as gold, silver, ruthenium, rhodium, palladium, osmium, iridium and platinum, and is a Co-Sn/NC catalyst, namely the active component of the catalyst is metal cobalt, the promoting component is tin, and the carrier of the catalyst is a nitrogen-containing carbon carrier.

The inventor of the invention finds that the nitrogen-containing carbon material carrier has stronger microwave absorption capacity. According to the invention, the active component and the catalytic promoter are loaded on the nitrogen-containing carbon material, so that the catalytic reaction bed of the composite non-noble metal catalyst can be stably maintained at a higher temperature level while the catalytic performance is stable.

In a specific embodiment, the content of the active component in the Co-Sn/NC catalyst is 1 to 50 wt%, preferably 1 to 7 wt%.

In one embodiment, the ratio of the amounts of active component to Co-catalytic component species in the Co-Sn/NC catalyst is 1: 1-5, preferably 1: 1.5 to 3.

In a specific embodiment, a reaction tube for filling the Co-Sn/NC catalyst is provided in the microwave reactor, and preferably the reaction tube is a quartz reaction tube.

In a specific embodiment, the propane content of the propane-containing gas is 2 to 100 vol%, preferably 5 to 15 vol%.

In a specific embodiment, the preparation method of the Co-Sn/NC catalyst comprises the steps of carrying out solvothermal reaction on an active component, a promoter component and a precursor of a carrier, and calcining and forming.

In a specific embodiment, the preparation method of the Co-Sn/NC catalyst further comprises the step of grinding the calcined and molded catalyst to screen out particles of 40-60 meshes to obtain the composite non-noble metal catalyst.

In a specific embodiment, the preparation method of the Co-Sn/NC catalyst further comprises adding zinc chloride for dispersing the cobalt source and the tin source, and the zinc chloride participates in the solvothermal reaction together with the active component, the promoter component and the precursor of the carrier.

In a specific embodiment, the temperature of the direct dehydrogenation of propane in the catalytic reaction bed is 300-680 ℃, preferably 350-550 ℃; the reaction pressure for producing propylene and hydrogen by dehydrogenation of propane is preferably normal pressure.

In a specific embodiment, the preparation method of the Co-Sn/NC catalyst comprises the steps of dissolving a cobalt source, a tin source and zinc chloride in a formamide solution in an ultrasonic mode, then transferring the solution into a high-pressure kettle to carry out solvent heat treatment to obtain a black solid, carrying out solvent heat reaction for more than 6 hours, and then treating the solid at a high temperature of 700-1000 ℃ for more than 2 hours in a nitrogen atmosphere to obtain the composite non-noble metal catalyst.

In a specific embodiment, the composite non-noble metal catalyst is filled into a reaction tube to form a microwave catalytic reaction bed, a temperature thermocouple is inserted in the middle of the bed layer, and quartz wool is filled at two ends of the bed layer for fixing.

Compared with the prior art, the invention has the following advantages: the invention solves the problem of lower activity of non-noble metal catalysts in the prior art. The method has the advantages of mild reaction conditions, high propane conversion rate and propylene selectivity, simple reaction operation, low energy consumption and low cost. The invention utilizes abundant alkane resources to prepare propylene and hydrogen, and maximally utilizes the alkane resources.

Drawings

FIG. 1 is an XRD pattern of the Co-Sn/NC catalyst prepared in example 1.

FIG. 2 is a TEM image of the Co-Sn/NC catalyst prepared in example 1.

FIG. 3 is an Element distribution diagram (Element mapping) of the Co-Sn/NC catalyst prepared in example 1.

FIG. 4 is a schematic view of a microwave reactor apparatus used in example 2.

In fig. 4, 1 propane gas circuit; 2, a nitrogen gas circuit; 3, storing liquid for standby; 4, a metering pump; 5, a mass flow meter; 6, a valve; 7 a premixer; 8 quartz tube reactor; 9 catalyst bed layer; 10 a thermal insulation layer; 11 a microwave resonant cavity; 12 a microwave generator; 13 gas analyzer.

Detailed Description

The following is described in further detail with reference to examples:

the method comprises the steps of filling a catalyst bed layer in a quartz reaction tube, introducing nitrogen to purge and remove air (for example, purging the nitrogen for 20min), and then irradiating by microwaves. A mixed gas containing propane (10 vol% of C was used in the present invention) was introduced into the reaction tube₃H₈And 90 vol% N₂The mixed gas of (2) was subjected to an experiment), the flow rate of the mixed gas containing propane was controlled by a rotameter, and propane was decomposed to produce propylene and hydrogen when passing through the catalyst bed. And (3) detecting propane and propylene generated after reaction in the outlet gas by using gas chromatography analysis, and calculating the propane conversion rate and the propylene selectivity according to the concentration of the propane and the propylene. The temperature of the direct catalytic dehydrogenation reaction is 300-450 ℃; the pressure of the direct catalytic decomposition reaction is normal pressure.

The main experimental instruments and raw materials in the following examples: the microwave catalytic reactor is a microwave catalytic reaction device shown in CN 102133516A, and in the microwave reactor, the power of microwave is continuously adjustable from 0W to 1000W, and the frequency is 2450 MHz. The quartz reaction tube had an outer diameter of 20mm, an inner diameter of 10mm and a length of 540 mm. The detection of propane and propylene was carried out by GC-6820A gas chromatography, manufactured by Agilent, USA. Propane gas was supplied by Dalian specialty gas Co., Ltd, and nitrogen gas was supplied by Special gas Co., West Hunan Tan. The carrier, the active component and the cocatalyst component can be obtained commercially or prepared in a laboratory, and the implementation of the method is not influenced.

Example 1

Preparation of the catalyst: 1.154g Co (NO)₃)₂·6H₂O、1.79g SnCl₂·2H₂O and 5.44g of zinc chloride were added to 400mL of formamide and sonication was performed for 30 min. Then transferring the uniform solution into a 500mL autoclave, heating at 180 ℃ for 12h, cooling, centrifuging the obtained black solid, washing with deionized water for 3 times, and drying at 80 DEG CAnd (5) drying. Then in a tube furnace, N₂Keeping the temperature of the protective atmosphere at 900 ℃ for 2h to obtain the Co-Sn/NC catalyst. During the high-temperature calcination process, zinc chloride added in the formamide solution is sublimated, so that the obtained catalyst does not contain zinc.

The solvothermal method used in the above preparation method is developed based on a hydrothermal method, and refers to a synthesis method in which an original mixture is reacted in a closed system such as an autoclave with an organic or non-aqueous solvent as a solvent at a certain temperature and a certain autogenous pressure of the solution. It differs from hydrothermal reactions in that the solvent used is organic rather than water.

FIG. 1, FIG. 2 and FIG. 3 are an XRD view, a TEM view and an Element mapping view of the Co-Sn/NC catalyst prepared in the example, respectively. From the XRD pattern of FIG. 1, it can be seen that the prepared catalyst contains simple substances Sn and SnO₂The most predominant of which is a crystalline phase of elemental Sn. Fig. 2 and 3 show that the C, N, Co and Sn are uniformly distributed in the catalyst prepared by us. It is presumed from fig. 2 and 3 that there is no reason why the Co peak is shown in XRD, because the content of Co is low and the dispersion is good so that the minimum detection limit of XRD is not reached. FIG. 3 fully illustrates the successful preparation of Co-Sn/NC catalysts in the present invention.

Example 2

This example examines the conversion of propane in propane-containing gas and the selectivity to propylene under microwave irradiation at different temperatures using a 3.2 wt.% Co-Sn/NC catalyst prepared as in example 1. The composite non-noble metal catalyst used in the embodiment has the mass of 1g, the flow rate of mixed gas at an inlet is 60ml/min, the reaction pressure is normal pressure, the microwave power is continuously adjustable within 0-1000W, and the frequency is 2450 MHz. The quartz reaction tube for the experiment has the outer diameter of 20mm, the inner diameter of 10mm and the length of 540 mm. The catalyst is filled in the quartz tube reactor to form a catalyst bed layer. The bed temperature was maintained at 300 deg.C, 350 deg.C, 400 deg.C and 450 deg.C, respectively, and microwave-catalyzed propane direct dehydrogenation was conducted to produce propylene and hydrogen, with the experimental results as shown in Table 1. The microwave apparatus used in example 2 is shown in fig. 4. The water flowing in figure 4 at the microwave resonance cavity 11 is used for cooling and absorbing the waves in the microwave reactor.

TABLE 1

At a catalyst bed temperature of 300 deg.c, the catalyst exhibits dehydrogenation activity, and at a catalyst bed temperature of 450 deg.c, the propane conversion on the catalyst increases to 15% and the propylene selectivity remains close to 75%. Under the condition of low temperature, the catalyst shows certain activity of catalyzing direct dehydrogenation of propane by microwaves, and the reaction temperature has obvious influence on the conversion rate of propane and the selectivity of propylene.

Example 3

This example examines the dehydrogenation conversion rate of propane and the selectivity of propylene in the mixed gas containing propane when the catalyst bed temperature is 450 ℃ in the catalysts with different active component contents prepared by the method in example 1, namely 6.4 wt% Co-Sn/NC, 3.2 wt% Co-Sn/NC, 2 wt% Co-Sn/NC and 1.2 wt% Co-Sn/NC. The mass of the composite non-noble metal catalyst used in the embodiment is 1g, the flow rate of mixed gas at an inlet is 60ml/min, the reaction pressure is normal pressure, and the experimental results are shown in table 2.

TABLE 2

As can be seen from the results in table 2, the content of active component in the catalyst has a significant effect on both propane conversion and propylene selectivity. Experiments show that the composite non-noble metal catalyst has a good catalytic effect when the cobalt content is 1-7 wt%, and particularly has a better effect when the cobalt content is 2-4 wt%.

The embodiment shows that the method for preparing propylene and hydrogen by combining the composite non-metal catalyst and the microwave field catalytic propane dehydrogenation is an effective and feasible method, and has the advantages of high dehydrogenation efficiency, quick reaction, simplicity in operation and low energy consumption under mild conditions. The invention is especially suitable for the treatment of natural gas, oil field and liquefied petroleum gas with rich propane content, and can prepare the shortage of propylene through propane dehydrogenation reaction.

Comparative example 1

TABLE 3

As can be seen from the results in Table 3, the use of 3.2 wt% Co-Sn/NC catalyst in the direct dehydrogenation of propane in the conventional reaction mode at a temperature of 450 ℃ has a conversion of less than 5% and a propylene selectivity of around 67%.

Comparative example 2

TABLE 4

As can be seen from the experimental results in Table 4, in the conventional reaction mode, when the Co-Sn/NC catalyst with the weight percentage of 3.2 is used for the direct dehydrogenation reaction of propane, the C-C bond is seriously broken and the selectivity of propylene is worse along with the increase of the temperature.

As can be seen from the above two comparative examples, the process of the invention operates at lower temperatures (450 ℃) than the prior art and also has a higher activity (15% propane conversion and 75% propylene selectivity).

Comparative example 3

Co-Sn/ZSM-5 was used as a catalyst, and the catalyst was prepared by a general impregnation method (the contents of Co and Sn in the catalyst were the same as in example 2). When the catalyst is used for catalyzing direct decomposition of propane under the same microwave reaction conditions as in example 2, experiments show that the temperature of the catalyst bed is difficult to rise, and the temperature is difficult to rise to 450 ℃. And when the temperature of the catalyst bed reaches 450 ℃, the conversion rate of propane for catalyzing direct decomposition of propane and the selectivity of propylene are very low, and are respectively 8.5 percent and 50 percent.

The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, several simple deductions and substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.

Claims

1. A catalytic decomposition method for preparing propylene by direct dehydrogenation of propane comprises the steps of forming a catalytic reaction bed by using a composite non-noble metal catalyst in a microwave reactor, and carrying out gas-solid phase microwave catalytic reaction on propane-containing gas through the catalytic reaction bed so as to realize the direct dehydrogenation of propane to prepare propylene; the composite non-noble metal catalyst does not contain noble metals such as gold, silver, ruthenium, rhodium, palladium, osmium, iridium and platinum, and is a Co-Sn/NC catalyst, namely the active component of the catalyst is metal cobalt, the promoting component is tin, and the carrier of the catalyst is a nitrogen-containing carbon carrier.

2. The catalytic decomposition method according to claim 1, wherein the content of the active component in the Co-Sn/NC catalyst is 1 to 50 wt%, preferably 1 to 7 wt%.

3. The catalytic decomposition method according to claim 1, wherein the ratio of the amounts of the active component and the Co-catalytic component in the Co-Sn/NC catalyst is 1: 1-5, preferably 1: 1.5 to 3.

4. The catalytic decomposition method according to claim 1, wherein a reaction tube for filling the Co-Sn/NC catalyst is provided in the microwave reactor, and preferably the reaction tube is a quartz reaction tube.

5. The catalytic decomposition method according to claim 1, wherein the content of propane in the propane-containing gas is 2 to 100 vol%, preferably 5 to 15 vol%.

6. The catalytic decomposition method according to claim 1 to 5, wherein the preparation method of the Co-Sn/NC catalyst comprises the steps of carrying out solvothermal reaction and calcination molding on the active component, the promoter component and the precursor of the carrier.

7. The catalytic decomposition method according to claim 6, wherein the preparation method of the Co-Sn/NC catalyst further comprises grinding the calcined and molded catalyst to obtain particles of 40-60 meshes, thereby obtaining the composite non-noble metal catalyst.

8. The catalytic decomposition method according to claim 6, wherein the preparation method of the Co-Sn/NC catalyst further comprises adding zinc chloride for dispersing the cobalt source and the tin source, and the zinc chloride participates in the solvothermal reaction together with the active component, the promoter component and the precursor of the carrier.

9. The catalytic decomposition process according to claim 1, wherein the temperature of the direct dehydrogenation of propane in the catalytic reaction bed is 300 to 680 ℃, preferably 350 to 550 ℃; the reaction pressure for producing propylene and hydrogen by dehydrogenation of propane is preferably normal pressure.

10. The catalytic decomposition method of claim 1, wherein the preparation method of the Co-Sn/NC catalyst comprises the steps of dissolving a cobalt source, a tin source and zinc chloride in a formamide solution in an ultrasonic mode, then transferring the formamide solution into a high-pressure kettle to carry out solvothermal treatment to obtain a black solid, carrying out solvothermal reaction for more than 6 hours, and then carrying out high-temperature treatment on the solid at 700-1000 ℃ for more than 2 hours in a nitrogen atmosphere to obtain the composite non-noble metal catalyst.